It is known to place such receiving antennas on the flanks of submarines. Their area is up to several square meters and they are called “flank arrays”. In French patent No. 92/06279 filed on May 27, 1992, published on Nov. 26, 1992 under No. 2 691 596 and granted on Apr. 28, 1995, the Applicant described a flank array composed of several rectangular panels matching the convex shape of the flank of the submarine. Referring to FIG. 2a of that patent, the panels are mounted on two rails 3, 4 so that the panels are not in contact with the hull, a sheet of water separating the panels from the hull. Thus, the transmission of flexure waves from the hull to the sensor is limited.
However, vibrations and resonances of the hull and of the ancillary structures of the submarine (especially those emanating from the machinery) continue to pass through the rails.
In addition, since the directivity of the sensors is, in open water, omnidirectional (they are short compared with the central wavelength of the listening frequency band), the hull cannot be clad with a low-acoustic-impedance baffle that would improve the acoustic stealth of the submarine, since the directivity would then be variable and not controllable.
To alleviate these drawbacks, the invention proposes to combine particle velocity sensors with the pressure sensors so that each receiving panel is directional.
To alleviate these drawbacks, the invention proposes a surface acoustic antenna, of the type comprising an array of plane pressure sensors made of a piezoelectric plastic that are fixed so as to be planar in a support structure, mainly characterized in that certain of these sensors are replaced with particle velocity sensors placed in such a way that the combination of the signal from the pressure sensors and the signal from the velocity sensors is used to obtain a cardioid having a zero for reception normal to one of the faces of the antenna.